Question

In C# 4.0, MemoryMappedFile has several factory methods: CreateFromFile, CreateNew, CreateOrOpen, or OpenExisting. I need to open the MemoryMappedFile if it exists, and if not, create it from a file. My code to open the memory map looks like this:

try
{
    map = MemoryMappedFile.OpenExisting(
        MapName,
        MemoryMappedFileRights.ReadWrite
        | MemoryMappedFileRights.Delete);
}
catch (FileNotFoundException)
{
    try
    {
        stream = new FileStream(
            FileName,
            FileMode.OpenOrCreate,
            FileAccess.ReadWrite,
            FileShare.Read | FileShare.Delete);
        map = MemoryMappedFile.CreateFromFile(
            stream, MapName, length + 16,
            MemoryMappedFileAccess.ReadWrite,
            null,
            HandleInheritability.None,
            false);
    }
    catch
    {
        if (stream != null)
            stream.Dispose();
        stream = null;
    }
}

It pretty much works the way I want it to, but it ends up throwing an exception on OpenExisting way too often. Is there a way to check whether the MemoryMappedFile actually exists before I try to do the OpenExisting call? Or do I have to deal with the exception every single time?

Also, is there a way to find out if the current handle is the last one to have the MemoryMappedFile open, to determine if the file will be closed when the current handle is disposed?

Answer 1

See Han Passant’s comment under the original question for accepted answer. Since I can’t mark it as accepted, I’ll just refer to it here and mark this as accepted.